Fitting arrangements for effecting a compressive sealed engagement to the end of a nonthreaded tube, particularly when the tube is constructed of metal or glass, have conventionally utilized a collar or nut disposed in surrounding relationship to the tube, with a tapered compression sleeve (conventionally referred to as a ferrule) cooperating therebetween to effect the desired sealed relationship around the tube. Similar such fitting arrangements have also been adapted for use with plastic tubes, although many such fitting arrangements have provided less than optimum results in view of the fact that plastic tube more readily deforms. Further, in many of the known fitting arrangements, once the fitting is disassembled and then reassembled, it has been observed that a proper compressive seal can no longer be obtained, and hence some leakage has been observed.
Another problem with the use of such fitting arrangements, particularly when used in conjunction with plastic tube, is the inability to securely lock the fitting in place inasmuch as plastic tube is very slippery and hence the fitting tends to slide axially therealong. To overcome this problem, one known fitting arrangement provides a separate gripper sleeve which is also disposed within the nut so as to be compressed against the tube, the gripper sleeve being axially split so as to be radially compressible and being provided with radially inward projections which effect localized deformation and hence gripping of the plastic tube.
The fitting arrangement employing a separate gripper sleeve, as described above, has been extensively commercially utilized by many manufacturers. In operation of this fitting, the gripper sleeve at one end has an exterior conical surface which is engaged with an opposed conical surface on the nut, and the gripper sleeve at its other end has an axial end face which abuts against an opposed axial end face on the ferrule. In theory, the ferrule is radially compressed by the tapered end of the fitting as the latter is relatively threaded axially into the nut, and the ferrule and nut in turn cooperate to axially compress and ultimately radially compress the gripper sleeve. In actuality, however, it has been observed that the gripper sleeve often affixes itself to the tube before it has moved forwardly into the nut a sufficient distance to permit the ferrule to be properly radially deformed into compressive sealing engagement with the tube. That is, the gripper sleeve tends to prematurely affix itself to the tube before the ferrule has been sufficiently radially compressed to permit sealing engagement with the tube, whereupon the gripper sleeve then interferes with and effectively prevents proper radial compression of the ferrule. Hence, a proper deformation of the tube by the ferrule, and thus creation of a proper seal, is not achieved. Fitting arrangements of this latter type have often exhibited leakage, and in fact a significant percentage of such fittings do exhibit leakage and often require replacement.
In an attempt to overcome the leakage problems associated with fitting arrangements of the above type, numerous variations have been made in the design of the gripper sleeve. For example, some fitting arrangements have constructed the gripper in the manner of a flexible collet. That is, the gripper sleeve is formed as a continuous ring having a plurality of circumferentially spaced slits, with alternate slits opening through one of the axial ends of the gripper sleeve, with the slits at their other end being closed. With such construction, however, it has been observed that proper sealing is still oftentimes difficult to achieve, and proper cooperative engagement of the gripper between the tube, nut and ferrule is not consistently achieved.
Accordingly, it is an object of this invention to provide an improved fitting arrangement constructed similar to the first aforementioned type, which fitting arrangement is capable of sealing aggressive fluids and gases throughout a wide temperature range without requiring special equipment or tube preparation.
More specifically, in the improved fitting arrangement of the present invention, the sleevelike gripping sleeve and ferrule axially cooperate with one another and within the threadedly engaged nut and fitting body. The ferrule, as is known, has a tapered outer surface which engages an opposed tapered inner surface on the fitting body, the taper on the ferrule being slightly less than the taper on the fitting body so that the leading edge of the ferrule is sealingly clamped against and into the wall of the tube. The gripping sleeve has an outer tapered surface surrounded by an inner tapered surface on the nut, with the taper on the gripper sleeve being slightly larger (such as by about 5.degree.) than the taper on the nut. The leading end surface on the gripper sleeve, namely the end surface which opposes and abuttingly contacts the end surface on the ferrule, is dished or angled by an amount similar to the differential between the tapers on the nut and gripper sleeve. Tightening of the nut onto the fitting body causes the inner taper on the nut to react against the taper on the gripper sleeve, which thereby effects an axial torsional distortion of the gripper sleeve so that the teeth thereon are forced into the wall of the tube, and at the same time the dished end surface of the gripper sleeve assumes a substantially flat condition wherein it abuts the opposed flat end surface on the ferrule. This rotational biting of the gripper sleeve into the tube can be effected while requiring little tightening force of the nut onto the fitting body. At the same time, the gripper sleeve, due to the axial torque imposed thereon by the nut, acts as a spring and exerts pressure against the opposed end face of the ferrule so as to sealingly clamp the ferrule between the fitting body and the tube.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.